Leak detectors with sniffing facilities are known (c.f., for example, DE-A 24 41 124 and DE-A 199 11 260). In the instance of sniffing leak detection, a unit under test containing a test gas is scanned with the aid of a sniffing tip. If a leak is present, test gas will escape to the outside. It is then supplied by the sniffing tip to a gas detector or gas sensor. The signals produced by the gas detector serve, among other things, the generation of alarm signals, preferably of the acoustic type. Frequently, helium serves as the test gas. Also a working gas present in any case within the unit under test may be employed as the test gas, in cooling facilities a halogen gas, for example.